I read somewhere that estriol is a safer estrogen. Is that true?
Although some people hold the opinion that compounded bioidentical hormones using estriol are safer for the breast, it is an unfounded claim. Estriol is the form of estrogen that is really only present in any appreciable amounts during pregnancy. Estriol is a much weaker estrogen than estradiol, the predominant circulating estrogen in young women. It is true that if you put the same amount of estradiol and estriol in a petri-dish with breast cancer cells, the cells exposed to estradiol would proliferate faster. However, if one places equipotent amounts of estriol and estradiol in their respective petri-dishes, the degree of proliferation would be the same. Bottom line: there is no evidence to support the theory that estriol is safer for the breast.
